Question

Which of the following statement is TRUE for the World Geodetic System 1984 (WGS84)?

• A. The WGS84 ellipsoid best fits the shape of the earth including its topography
• B. The WGS84 ellipsoid and the Geodetic Reference System 1980 (GRS80) ellipsoid are one and the same
• C. The WGS84 ellipsoid is not a geocentric ellipsoid
• D. The WGS84 ellipsoid can be used to determine the geoid

Hint:

Remember the three surfaces: {Topography} (actual terrain), {Geoid} (equipotential, “mean sea level”), and {Ellipsoid} (smooth reference). WGS84 provides the global {geocentric ellipsoid} and frame; geoid models give $N$ above/below that ellipsoid.

Answer 1

The Correct Option is D

(A) False. An ellipsoid is a smooth mathematical surface approximating the Earth; it does not include the terrain/topography. WGS84 defines a reference (best–fit, global) ellipsoid, not a topographic surface.
(B) False. WGS84 and GRS80 are very close but not identical (slightly different defining constants/realizations). Saying they are “one and the same” is inaccurate.
(C) False. WGS84 is explicitly geocentric (Earth-Centered, Earth-Fixed frame).
(D) True. The geoid is determined relative to a reference ellipsoid. Using the WGS84 ellipsoid (together with a gravity model) one computes geoid undulation $N$ and thus the geoid. Hence WGS84 can be used to determine the geoid surface.
\[ \boxed{\text{(D)}} \]